This invention relates to the measuring and recording of the settling behavior of certain liquid-solid mixtures and, more particularly, relates to the automatic recordation of sedimentation phenomena in blood samples.
Heretofore observation of sedimentation phenomena in blood samples has been carried out basically through two techniques known as the Wintrobe method and the Westergren method. These techniques involve the manual observation and recordation of the settling behavior of the red cells of a blood sample contained in a glass tube of standardized dimensions. As the red cells settle out, the separation boundary between the cells and the clear plasma fluid is observed against a calibrated scale provided on or adjacent to the tube. One or two readings are manually taken as settling progresses over a one to two hour period. According to the usual procedure, a first reading is taken after one hour and a second after two hours, the latter in most cases representing the maximum settling point of the sample.
These procedures provide only a small amount of insight into the settling phenomena as they record only two widely spaced points on the curve. They are further subject to the inaccuracies inherent in human observation and measurement.
Of the automatic sedimentation recorders devised to date none have provided a highly accurate, continuous record of the settling process from beginning to end. A typical technique used for automatic recording has been to direct an image of the settling tube onto a moving sheet of photosensitive paper. The solid-liquid separation boundary within the tube traces a line on the paper which, on development, gives a visible display of the settling phenomena. A drawback of this system is that photosensitive paper is expensive and difficult to work with and requires the use of complex light-tight enclosures as well as a separate development step at the end of the process. Further, it is difficult to obtain a crisp, well defined settling trace with this type of photographic system.